In a study of 179 women with colon cancer, 34% of those taking Avastin as an add-on to chemotherapy developed amenorrhea, a condition in which menstruation has ceased for three or more months, compared to 2% among those not taking the drug.

Of the women who experienced ovarian failure, 22% began menstruating again after they stopped taking Avastin.

The label tells patients: "Long term effects of Avastin exposure on fertility are unknown." The label advises doctors to discuss risks with patients prior to treatment with Avastin.

About Avastin

In June 2011, an FDA advisory panel recommended that Avastin no longer be sold as a treatment for breast cancer.

Injected every two to three weeks, Avastin works by blocking the production of blood vessels that would otherwise supply tumors with oxygen and nutrients. This slows the growth and spread of tumors. It is taken in addition to chemotherapy.

Avastin Risks

Ovarian failure was not the only warning added to the new label. Some patients taking Avastin reportedly developed osteonecrosis of the jaw, a condition in which a lack of blood flow causes bone to die. According to the FDA, the cause is unclear. But it's possible that Avastin's mechanism to prevent the formation of blood vessels may have blocked blood flow to tissue in the patients' jawbones.

The FDA reports that a new study shows further evidence that Avastin may increase the risk of blood clots associated with venous thromboembolic events (VTE), such as deep venous thrombosis and pulmonary embolism.

More than 1,400 patients with colorectal cancer that had spread participated in the study. Of those, 13.5% of those taking Avastin had some sort of VTE compared to 9.6% of patients on chemotherapy alone. After being treated with anti-clottingdrugs, those on Avastin were more likely to have another VTE or to experience bleeding.